PULSATING-DIAPHRAGM FUEL
PUMP
Pulsating-diaphragm fuel pumps, or pulse pumps, rely
on changes in crankcase vacuum to create a pulsating
movement of the pump diaphragm.
As
the engine's
pistons move outward, a vacuum is created. This
vacuum is transmitted
to
the pump diaphragm causing it
to pull back and suck fuel into the pump.
As
the engine's
pistons move inward, crankcase vacuum is reduced
and the diaphragm return spring pushes the pump
diaphragm forward, forcing fuel through the pump
outlet.
Fuel
Pump
Test
Procedure
Before testing make certain the fuel pump vacuum and
fuel line connections are tight and free
of
leaks.
1.
Operate engine at an idle for five minutes to ensure
that carburetor is
full
of
fuel.
lgnifion
of
fuel can result in
@!!@%I
severe personal injury or death.
Thoroughly clean
up
any spilled fuel.
2.
Shut engine
off
and remove fuel inlet line from fuel
Pump.
Ignition of fuel can result in
laWAR"G1
severe personal injury or deafh.
Thoroughly clean
up
any spilled fuel.
7.
Remove fuel outlet line from fuel pump.
8.
Connect a pressure gauge to fuel pump outlet using
a piece of fuel hose with clamps.
9.
Start engine and allow to idle for at least five
seconds. While holding pressure gauge level with
pump outlet record pressure gauge reading.
10.
Move throttle control
to
high idle position and allow
engine
to
run for at least five seconds. While holding
pressure gauge level with pump outlet record
pressure gauge reading.
11.
Shut engine
off
and remove pressure gauge hose
from fuel pump outlet. Connect fuel outlet line tofuel
Pump.
Replace the fuel pump if test readings are not within the
values specified in TABLE
1.
TABLE
1
PULSE PUMP
TEST
SPECIFICATIONS
3.
Connect a vacuum gauge tofuel pump inlet using
a
piece of fuel hose with clamps.
4.
Start engine and allow to idle for at least five
seconds. Record vacuum gauge reading.
5.
Move throttle control to high idle position.
Wait
at
least five seconds and record vacuum gauge
reading.
6.
Shut
engine
off
and remove vacuum gauge hose
from fuel pump inlet. Connect fuel inlet line
to
fuel
pump.
ENGINE PUMP INLET PUMP OUTLET
SPEED VACUUM PRESSURE
(Minimum) (Minimum)
Low Idle
2.6
inches 1.7 psi
of mercury
High Idle 2.6 inches 1.7 psi
of mercury
7-4
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